Known types of angular velocity sensors include a floating comblike electrode (with one set of comb fingers or segments) at the left latus part of a floating thin film and a floating comblike electrode (with one set of comb fingers) at the right latus part of the floating thin film (left floating comb-like electrode and right floating comb-like electrode). Fixed comblike electrodes are provided and have two sets of comb fingers, a left fixed comb-like electrode and a right fixed comb-like electrode whose fingers interdigitate with the respective sets of fingers of the left and right floating comb-like electrodes in a non-contacting parallel fashion. The floating thin film is vibrated in an x-direction by applying voltages alternately between the left floating comb-like electrode and the left fixed comb-like electrode, and between the right floating comb-like electrode and the right fixed comb-like electrode. When the angular velocity of rotation about a z-axis acts on the floating thin film, this floating thin film is subjected to a Coriolis force, and the floating thin film undergoes an elliptic vibration in which it is also vibrated in the y-direction. When the floating thin film is made of an electric conductor or when an electrode is joined to the floating thin film, and when a detection electrode parallel to the xz-plane of the floating thin film is disposed on a substrate beforehand, the capacitance between the detection electrode and the floating thin film fluctuates or changes in correspondence with the y-component (angular velocity component) of the elliptic vibration. The angular velocity can be found by measuring the change (amplitude) of the capacitance. Angular velocity sensors of this type are described in, for example, Japanese Patent Application Laid-Open No. 248872/1993, Japanese Patent Application Laid-Open No. 218268/1995, Japanese Patent Application Laid-Open No. 152327/1996, Japanese Patent Application Laid-Open No. 127148/1997, and Japanese Patent Application Laid-Open No. 42973/1997.
U.S. Pat. No. 5,635,638 discloses an angular velocity sensor in which, as shown in FIG. 4 of the patent, a pair of vibrators are coupled by a pair of semicircular beams, with the pair of vibrators being supported by eight anchors through the beams which are highly flexible or bendable in the vibrating direction x of the respective vibrators.
The angular velocity sensor has separate multipoint anchor portions which are distant from one another. Therefore, when subjected to an external force associated with a temperature change or the like, each of the beam spring portions for moving the vibrator as a simple harmonic motion undergoes a compressive or tensile stress. For this reason, the resonance frequency of the vibrator changes with temperature and exhibits hysteresis characteristics having discontinuous points. This undesirably lowers the precision of the sensor.
With known angular velocity sensors having separate multipoint anchor portions as disclosed in, for example, Japanese Patent Application Laid-Open No. 218268/1995, it is found that the vibration of the vibrator during driving operation will leak into the vibration at the detection side due to the distant anchor portions, and so the precision will lower. Also, with the known angular velocity sensor in which the immobile points of a driving vibration mode and a detecting vibration mode do not coincide, as disclosed in, for example, Japanese Patent Application Laid-Open No. 218268/1995, it is found that the detection precision for an angular velocity will be reduced under the influences of the external force and the vibration leakages between the two modes. Moreover, when a vibrating component diminishing the vibration based on the Coriolis force is contained in the driving vibration mode, the detection output of the angular velocity is small. In this regard, there is an occasion where the vibration of the vibrator in the prior art becomes unstable due to different amplitudes in the +x-direction and -x-direction, and this is undesirable.
With the angular velocity sensor disclosed in U.S. Pat. No. 5,635,638, oscillating springs are not connected to the center of gravity of each of the vibrators. It is therefore conjectured that the vibrations of the vibrators will become unbalanced when drive forces exerted on oscillating masses are nonuniform due to a discrepancy in manufacturing dimensions. Additionally, the vibrations become nonlinear. The unstable fluctuations of the detection outputs are accordingly incurred by the unbalance of the shift fluctuations of the resonance frequencies of the vibrators, and so the S/N ratio (signal-to-noise) of the angular velocity signal will be inferior. Also, because a vibration driving signal travels to a detecting capacitor, the S/N ratio of the angular velocity signal will be lowered. Further, with the known sensor, leakage of the driving oscillation flow as leakage signals to the respective detecting portions. In this regard, because electrical distances and geometrical distances from an oscillating portion to the respective detecting portions are not symmetrical, the leakage signals cannot be eliminated even by contriving or providing the operations of an electric circuit portion. A degradation in the S/N ratio is thus brought about.
In light of the foregoing, a need exists for an angular velocity sensor that is able to prevent the detection precision from being lowered due to physical (electrical and mechanical) disturbances.
A need also exists for an angular velocity sensor that is able to suppress the degradation of the signal-to-noise ratio associated with leaks of the vibration driving signal, to thereby heighten the detection precision for the angular velocity sensor.